1. Field of the Invention
The present invention relates to a liquid medicine injection apparatus and more particularly to a liquid medicine injection apparatus that is adapted to inject a liquid medicine into blood vessels, the outside of an epidural space, the subcutaneous tissue, the bladder and the like by making use of a negative pressure.
2. Prior Art
In order to inject a predetermined quantity of liquid medicine into blood vessels and the like, it has been usual to use a syringe pump or a balloon infuser.
However, the syringe pump has the disadvantages that it has a complicated structure and is expensive while the balloon infuser has the disadvantage that since a liquid medicine which fills the balloon is expelled by the contracting force of the expanded balloon which is made of a rubber material, the discharge power is not kept constant.
Therefore, as a means for eliminating such disadvantages, there has been proposed a liquid medicine injection apparatus which is simple in structure and inexpensive and whose medicine discharge power is constant (as disclosed in International Publication No. WO95/28977). As shown in FIG. 6, this apparatus comprises a barrel 130, a first gasket 140 capable of sliding within the barrel 130, a cylinder 210 integrally connected to the barrel 130 and a second gasket 220 slidably and liquid-tightly inserted into the cylinder 210. Further, the first gasket 140 and the second gasket 220 are connected to each other through a plunger 250 so that when barrel 130 is filled with a liquid medicine, the second gasket 220 interlocks with the first gasket 140 to slide within the cylinder 210 thereby reducing the pressure in the cylinder 210.
However, in the case of the above-described liquid medicine injection apparatus, since the first gasket 140 and the second gasket 220 are connected to each other by means of the plunger 250, when the liquid medicine is filled into the barrel 130, the plunger 250 is pulled against the negative pressure in the cylinder 210 and, therefore, a considerable degree of force is required for filling the barrel with the liquid medicine.